X-ray computed tomography (CT) scanners have been used for over twenty-five years to create images of cross-sectional slices of subjects, such as human patients, and are particularly used as a medical diagnostic aid. An x-ray CT scanner can produce a 3-dimensional anatomic image of a patient's body, as opposed to just a 2-dimensional image provided by a standard x-ray machine.
An annular gantry normally supports many of the components of an x-ray CT scanner and includes an outer ring secured to a stand and an inner ring mounted for rotation within the outer ring. During a scanning procedure, a patient table is positioned through the center of the gantry, the inner ring is rotated about the table and an x-ray beam is passed through center of the gantry from the spinning inner ring. The components supported by the gantry can include an x-ray tube for providing the x-ray beam, one or more high voltage power supplies, balancing weights, a data acquisition module, and a bank of detectors diametrically opposed from the x-ray source. At least some of these components are secured in the inner ring for rotation therewith.
Positron emissions tomography (PET) scanning is a more recently developed procedure that uses positron emitting radioactive isotopes to show function or metabolism, rather than anatomy as in x-ray CT scanning techniques. A PET scanner is made up of special radiation detectors called scintillators which are arranged in a ring configuration within an annular gantry. Basically, each detector has an associated partner detector oppositely located on the ring. This setup allows for the sensing and measurement of positrons emitted by radioactive isotopes injected into a patient. The measurements are processed through nuclear counting equipment and computers to produce 3-dimensional images that allow quantization of the physiochemical process in the patient's body. PET scanners are used to diagnose and monitor cancer, in addition to diseases of the heart, brain and lungs.
Recently, the results of different types of scanning procedures, e.g., PET and x-ray CT scans (and MRI and x-ray procedures), have been combined, or superimposed, to take advantage of the particular benefits of each procedure. Accordingly, a patient is first scanned using a first procedure, then scanned using a second procedure, and the results of both scans are combined using specialized software and computing systems.
In order to obtain tomographic images of a patient with either scanner, it is necessary that the patient be located exactly at a predetermined position inside the opening of an annular scan gantry of the apparatus. For this reason, such scanners have been provided with a patient handling couch or table which is moveable vertically to be in line with an axis of the scan gantry, and moveable axially in and out of the scan gantry. Some existing systems include a patient support couch or table that is movable between two or more separate scanning machines, such as an x-ray CT scanner and a PET scanner.
What is still desired, however, is a new and improved gantry that supports the components of at least two scanning machines, such as an x-ray CT scanner and a PET scanner. In this manner a patient can be successively scanned by two types of scanning machines by simply repositioning (i.e., moving horizontally) the patient in the same gantry between the components of the two scanning machines.